Ignition aid



July 3, 196.2- c. B. HENDERSON ETAL 3,041,835

IGNITION AID 2 Sheets-Sheet 1 Filed Feb. 5, 1959 AGENT ga rifflvnrfldwJuly 3, 1962 c. B. HENDERSON ETAL 3,041,835

IGNITION AID 2 Sheehs--Sheei'I 2 Filed Feb. 5, 1959 INVENTOS ZM/'ks/Zemdezwl @I ae M ,5l/fiala BY f5 m W AGENT nited 3,641,835 PatentedJuly 3, 1962 ration, f

This invention relates to a method and device for shaping and ignitingthe leading face of a column or mass of plastic monopropellant extrudinginto the combustion chamber of a gas generating apparatus, such as arocket motor or gas turbine.

The term monopropellant refers to a composition which is substantiallyself-sufficient with regard to its oxidant requirements as distinguishedfrom bipropellants where the fuel is maintained separately from theoxidizer source until admixture at the point of combustion.

There have recently been developed for use in gas generating apparatus,such as rocket motors, gas turbines and the like, a number of plasticmonopropellants, which are particularly adapted for extrusion ascohesive, shape-retaining, continuously advancing masses or columns intoa combustion chamber, where they are burned to generate high energygases for developing thrust or power or for providing heat or gaspressure. The compositions have thixotropic properties and aresuliciently iluid above a certain finite stress to be fed at ambienttemperatures through shaping apertures into a combustion chamber. Theleading face of the shape-retaining column presents a burning surface ofpredeterminable area, which can be varied and controlled by varying therate of extrusion. These plastic monopropellants combine many of theadvantages and eliminate many of the disadvantages of previously knownliquid or solid propellants used to power similar devices.

Such plastic monopropellants are normally stored in a fuel tank fromwhich they are extruded through an apertnred plate or other suitableextrusion member into a combnstion chamber. The primary purpose of theextrusion member is to divide the propellant into a plurality ofseparate masses or columns, thereby to increase the total burning areaof monopropellant available in a combustion chamber, of preferablyminimum length.

When burning equilibrium is reached at a given rate of extrusion, whichshould be higher than the linear burning rate of the monopropellant, theextruding column of monopropellant burns on all surfaces exposed in thecombustion chamber and these surfaces converge in the clownstreamdirection forming a downstream edge or apex, depending on the shape ofthe extrusion orice. The angle of convergence at equilibrium isdetermined only by the ratio of the linear rate of extrusion to thelinear burning rate of the particular monopropellant, regardless of thesize of the extrusion aperture. The higher the value of this ratio, themore acute is the downstream angle of convergence resulting in a longercolumn of burning propellant having a proportionally larger burningsurface area. The mass rate of burning is proportional to the burningsurface area and to the linear burning rate. Consequently, the linearrate of extrusion is, at equilibrium, the deterrninative factor for themass rate of burning.

Prior to ignition, the plastic monopropellant is ordinarily extrudedfrom the fuel tank into the extrusion member sufficiently completely toll the extrusion passages or orifices and to protrude into thecombustion chamber for a short distance beyond the downstream end of theorifice, the length of protrudnig column being predetermined by suchfactors as the linear burning rate of the particular monopropellantcomposition, the desired equilibrium burning surface area, the linearrate of extrusion during burning, the desired start-up pressure-timecharacteristics, and the change in mass rate of gas-generation and,thereby pressure, as the initially ignited burning surface approachesthe equilibrium burning surface.

The protruding portion of the monopropellant mass or column, prior toignition, will have a cross-sectional geometry similar to that of theextrusion orifice, which functions, in eifect, asl a shaping orifice,and a plane-surfaced leading face. The plane-surfaced protruding columncan be ignited by conventional methods, such as :a hot wire igniter, asquib, or the like. Ignition generally occurs iirst on the leading planesurface followed by ignition of the sides of the monopropellant columnexposed in the combustion chamber. In some cases ignition of the sidesmay not occur until combustion chamber temperature and pressure havereached a relatively high value. There is also the possibility, in someinstances, that the llame will not propagate down the sides before thelength of the column, which, while burning on its plane surface at thelinear lburning rate of the monopropellant, is being extruded at ahigher rate, becomes so excessive as to result in slumping,fragmentation, or even protrusion out through the gas venting nozzle.After burning propagates down the sides, the surfaces converge in thedownstream direction, as aforedescribed, eventually producing theequilibrium burning surface. In many applications, it is desirable, forsmooth performance, to achieve the equilibrium mass rate of gasgeneration and combustion chamber pressure as quickly as possibly, sothat the marked hiatus between ignition of the plane-surfacedmonopropellant column and formation of the equilibrium burning surfaceis disadvantageous. To some extent, this can be counterbalanced bycareful presetting of the initial degree of protrusion of themonopropellant into the cornbustion chamber prior to ignition and veryclosely regulated initial extrusion rate. However, this requiresexceedingly ne and critical prescheduling and manipulation. There is thelikelihood that equilibrium combustion chamber pressures will be reachedtoo slowly or may 1go through a transient overshoot. In some cases, oneor the other of these conditions may be desirable, but here again, thefine manipulation required to obtain the exactly desired programming isexceedingly diicult to achieve when the initial ignition surface of theplastic monopropellant is plane.

The object of this invention is to provide as an igniter for the plasticmonopropellant, a wafer of solid propellant so positioned relative tothe column of plastic monopropellant preliminarily extruded into thecombustion chamber prior to ignition, that the wafer functions both toignite the plastic propellant and to bring it very rapidly to burningsurface equilibrium.

Other objects and advantages of the invention will be made obvious bythe following detailed description taken in connection Iwith theaccompanying drawings in which like reference characters refer to likeparts throughout and wherein:

FIGURE 1 is a diagrammatic section view of the rear portion of a rocketengine in which the present invention nds application.

FIGURE 2 is a cross-sectional view taken along lines 2-2 of FIGURE 1showing the igniter wafer with a portion cut away to show the extrusionplate.

FIGURE 3 is a fragmentary view showing equilibrium burning afterignition of the solid and plastic propellants shown in FIGURE l.

FIGURE 4 is a plan view of a different embodiment of the invention.

FIGURE 5 is an isometric view of still another embodiment.

FIGURE 6 is a fragmentary longitudinal section along lines 6--6 ofFIGURE 5, showing the plastic mono- 3 propellant extruded downstream ofthe wafer orifice prior to ignition.

FIGURE 7 is a plan view of a modified form of the invention, showingsingle-orificed annular wafers.

FIGURE 8 is a plan view of a modification showing sealing closure of thedownstream ends of the solid propellant Wafer orifices.

FIGURE 9 is a longitudinal section along lines 9 9 of FIGURE 8.

Broadly speaking, the invention comprises a wafer of readily ignitiblesolid propellant mounted on the downstream face of the extrusion memberor plate, namely the face exposed to the combustion chamber, the waferbeing provided with an orifice positioned in registry with the extrusionmember orifice through which the plastic monopropelliant is yfed fromthe fuel chamber. The wafer orifice is, like the extrusion memberorifice, axially oriented in the `downstream direction of plasticmonopropellant fiow. Its cross-sectional area is at least as large asthat of the extrusion member orifice and is preferably the same,although it can be somewhat larger. The interior walls of the igniterwafer orifice should be parallel to the direction of propellant flowand, thereby, to the lateral walls of the extruded column of plasticpropellant prior to ignition. The cross-sectional geometry of the waferorifice is preferably substantially the same as that of the extrusionmember orifice. Small differences in geometry and cross-sectional areacan be tolerated so long as there is no overlapping of the wafer overthe extrusion member orifice to produce an obstruction to fiow.

The wafer orifice can be open to the combustion charnber at itsdownstream end or can be sealed by means of a transverse closure wallmade of the solid propellant. Alternatively, a thin sheet of an inert(namely non-selfoxidant) solid material, such fas cellophane, can belaid over the wafer orifices. Such an inert protective covering ispreferably not bonded to the solid propellant surface to 4avoid itshaving `an inhibiting effect. It should also be very thin so that itwill decompose or be torn away upon ignition of the conventional igniteremployed to ignite the solid propellant wafer.

The igniter wafer can be of a cross-sectional area sufficient to overliesubstantially the entire downstream face of the extrusion plate, withwafer orifices in registry with each of the extrusion orifices; orsufiicient to overlie just a portion of the plate, with wafer orificesin registry only with those extrusion orifices present in that portionof the extrusion plate; or suliicient only to provi-de a registeringwafer orifice for a single extrusion plate orifice. In some cases, itmay be ladequate to provide only some of the plastic monopropellantcolumns extruding through the extrusion orifice with the circumscribingsolid propellant. The igniter wafer, 4because of its position on theface of the extrusion plate at a level adjacent to the bases of theplastic propellant columns, is most suitably located to provide hotcombustion gases which circulate down between the uncircumscribedcolumns to ignite them laterally. The very rapid initiation ofequilibrium burning of the warfer-circumscribed plastic propellantcolumns hastens the build-up of temperature, pressure, and hotcirculating combustion gases, which also promote ignition.Single-orificed igniter wafers can be employed to fcircumscribe one orseveral of the plurality of extrusion orifices in an extrusion plate.

For most efficient action, all surfaces of the solid propellant wafersare inhibited against burning except the downstream face. In thepreferred embodiment, therefore, the lateral surfaces of the wafer,including the walls of the wafer orifice, `and its upstream base areinhibited. Inhibition can be accomplished in any conventional fashion,as by the application of a `coating of an inert polymer, such aspolyvinyl chloride or cellulose acetate, free from oxidizer.

The igniter wafers can be attached to the face of the extrusion plate inany convenient manner, as by bonding with a suitable adhesive which alsofunctions as a surface inhibitor.

in practice, prior to ignition, the plastic monopropellant is extrudmlfrom the fuel chamber through the extrusion member into the waferorifice to or beyond the downstream end of the wafer orifice, Afterignition by ya conventional igniter, such as a hot wire or squib, thesolid propellant wafer functions to ignite the plastic propellantbecause the hot combustion products produced immediately adjacent to theplastic propellant are above its ignition temperature. The leading planesurface of the plastic propellant column ignites practicallysimultaneously with ignition of the solid propellant.

To obtain the desired lateral ignition and downstream convergence of theburning lateral surfaces of the leading end of the plasticmonopropellant column essential to formation of the equilibrium burningsurface, at least some lateral surface, upstream from the initialplanesurfaced leading face of the plastic propellant column, must beexposed to ignition by the circumscribing solid propellant, which isburning in a linear direction upstream from its original uninhibitedburning surface. Any degree of such exposure Aaccompanied by lateralignition facilitates generation of the equilibrium burning surface. Thiscan be achieved by selection of a solid propellant material having asuitable linear burning rate relative to that of the plasticmonopropellant, by preliminary adjustment of the relative downstreamlevels of the igniter wafer and the plastic propellant column, or by acornbination of both of these factors.

`Where the solid propellant has a higher linear burning rate than theplastic propellant, it is obvious that after ignition, it will retreatupstream at a lfaster rate than the plastic propellant. if the plasticpropellant is initially extruded to a level flush with the downstreamend of the wafer orifice, Within which it is contained, after ignitionof the downstream faces, the burning surface of the solid propellantwafer retreats upstream more rapidly than that of the plastic propellantcolumn, thereby exposing to ignition lateral surface of the latter andinducing convergence. The higher the ratio of solid propellant linearburning rate to the plastic propellant linear burning rate, the morerapidly is the equilibrium burning surface configuration achieved.

The parameters, in terms of relative burning rates of the twopropellants, wafer thickness and extrusion orifice diameter can readilybe calculated `by those skilled in the art. To obtain a desiredcone-shaped equilibrium burning surface, for example, the relationshipof the burning rates, wafer thickness and orifice diameter can bedetermined as follows:

T0=time at ignition of the plastic propellant Tc=time at formation ofthe perfect cone, namely formation of the equilibrium cone anglet=thickness of solid propellant wafer d=idiameter of extrusion orificers=burning rate of solid propellant rp=burning rate of plasticpropellant therefore Since, starting with initially flush propellantlevels, the burning rate of the solid must be higher than that of theplastic to provide for lateral exposure of the latter, wafer thicknessmust be larger than extrusion orifice diameter in at least the sameratio `as the solid to plastic burning rates, and can be calculated forformation of the equilibrium cone from the foregoing mathematicallyexpressed relationship.

The above embodiment, namely initially fiush propellant levelsaccompanied by a ratio of solid to plastic propellant burning rategreater than 1, produces most rapidly a substantially perfectly shapedequilibrium burnning surface. Very satisfactory results in terms ofinitiation of convergence and rapid effectuation of the equilibriumburning surface can, however, be achieved by extrusion of the plasticpropellant prior to ignition for a predetermined distance beyond thedownstream level of the wafer. This expedient pre-exposes lateralplastic propellant surface to ignition by the hot combustion products ofthe ignited solid propellant wafer. Under these circumstances, thelinear burning rate of the solid propellant can be the same as that ofthe plastic propellant, or higher or lower within calculable limits.Here again, the required degree of plastic propellant protrusion and thethickness of the wafer for optimum performance can be calculated fromthe known burning rate and extrusion orifice diameter parameters.

Although certain predetermined ratios of the aforedescribed parametersprovide optimum performance in terms of rapidity of equilibrium burningestablishment, it is repeated that any degree of lateral ignition anddownstream convergence of the leading end of the plastic monopropellantcolumn ensures and hastens burning equilibrium. This is a practicaladvantage since it makes possible the use, within fairly broad limits,of the same available igniter wafer, suitably designed with an orificeor a plurality of orifices which can be placed in registry with anextrusion plate orifice or orifices, with different plasticmonopropellants or with the same plastic monopropellant at a differentprescheduled rate of extrusion and, therefore, different equilibriumburning surface.

In addition tofunctioning as an ignition and shaping aid, the solidpropellant wafer generates hot combustion gases which speed build-up tothe desired equilibrium combustion chamber pressure. A desiredpressure-time curve can be prescheduled by varying the initialuninhibited burning surface area of the solid propellant and thereby,the mass rate of gas generation with a given propellant. Total burningsurface area can, for example, be maximized by extending the wafer overthe entire downstream surface of the extrusion plate, with, of course,properly mating orifices. A reduction in burning surface area can beachieved by reducing the cross-sectional area of the wafer relative tothat of the extrusion plate or by employing a plurality ofsingle-orificed wafers applied to selected extrusion plate orifices. Thelinear burning rate of the solid propellant at initial and increasingpressures is also a factor in determining the rate of pressure build-upand this, in turn, may be a factor in determining the particularpractical ratio of the solid propellant linear burning rate relative tothat of the plastic monopropellant.

Onsetrof extrusion of the ignited plastic monopropellant column into thecombustion chamber should be delayed until at least a substantial degreeof downstream convergence. has taken place, the optimum time being atthe closest approach to equilibrium burning surface achievable under thegiven conditions prior to complete consumption of the solid propellant.

The plastic monopropellants, though cohesive and shape-retentive, willflow under stress, so that there may be some undesirable leakage intothe combustion chamber .after a long period of storage at attitudespromoting ow under the stress of the propellants own weight or understresses incident to handling or transportation. Some of the plasticmonopropellant compositions tend to be hygroscopic, namely to absorbatmospheric moisture which may adversely affect their viscosity andburning properties. A protective closure or seal can be provided at thedownstream end of the wafer orifice in the form of a layer of the solidpropellant or of a non-selfoxidant material, such as a solid polymer, asaforedescribed. Where a solid propellant closure is used, it can be madeintegral with the igniter wafer. After ignition, the relatively thinclosure layer burns down to the leading plane surface of the plasticpropellant column, and ignites it.

Turning now to the drawings and, in particular to FIGURE l, there isshown a diagrammatic longitudinal view of the rear portion of a rocketengine of the type which, by way of example, is adapted to use theignition device of the present invention. The rocket engine consists of`a fuel tank 1 which is of generally cylindrical shape and whichcontains a plastic monopropellant 2. Slidably mounted in the forward endof the fuel tank is an extrusion piston 3 which extrudes themonopropellant 2 through an extrusion member 4 into a combustion chamber5. Nozzle 6 is in open communication with the combustion chamber toreceive the gases generated therein and to discharge them to producethrust. The piston 3 is actuated by pressurized gas, such as nitrogen,admitted into the forward portion 7 of fuel tank 1 from a storage tankof the pressurized gas not shown. The pressure of gas applied -to piston3 and hence the rate of plastic monopropellant extrusion can becontrolled and varied by valve means also not shown. A conventionaligniter 8 is provided in the combustion chamber to ignite the wafer ofsolid propellant 9.

Extrusion plate 4 is provided with axial orifice passages lfl and l1 ofcircular cross section. A wafer of solid propellant 9 overlies theentire downstream face of extrusion plate 4 and is provided withcircular orifices 10a and lla in registry with extrusion plate orifices10 and il. The solid propellant igniter wafer 9 is adhesively bonded tothe extrusion plate and is provided with an inhibitor coating 12 on allexposed surfaces, including the walls of the wafer orifices, except forits downstream initial burning surface 13. The plastic monopropellant 2,prior to ignition, is extruded downstream to the point where its planeleading surface 14 is flush with the downstream surface 13 of the solidpropellant Wafer.

In this embodiment, it is essential that the burning rate of the solidwafer exceed that of the plastic propellent. For perfect equilibriumcone formation, the thickness of the wafer should exceed the diameter ofeach of the orifices in at least the same ratio as rs/rp. By satisfyingthis requirement for the larger orifices 10, a wafer of the same webthickness automatically satisfies this requirement for the smallerorifices. The wafer thickness can, of course, be reduced in the area ofthe smaller orifices to provide the same relationship of wafer thicknessto orifice diameter as in the case of the larger orifices, but this isnot essential.

FIGURE 3 shows the equiangled cones 15 and 16 formed at equilibriumburning a short time after ignition of solid propellant wafer and theleading end of the plastic monopropellant column. The solid propellantwafer has been largely, but not completely consumed. Extrusion of theburning, shaped plastic propellant columns into the combustion chambercan most effectively commence at the point shown.

FIGURE 4 shows the downstream face of an extrusion plate 4 having anextrusion orifice geometry similar to that of FIGURE 2. The igniterwafer 17, however, differs in covering only the central portion of theface of the extrusion plate and having wafer orifices 11a in registryonly with the central seven extrusion plate oriices.

Extrusion plate orifice geometry can be varied in a multitude of waysdetermined by such factors as the desired ratio, for a givenapplication, of total extrusion orifice cross-sectional area toextrusion plate cross-sectional area.

It is essential only that the solid propellant wafer be designed withmating orices. One of many available variations in extrusion orificegeometry is illustrated in FIGURE 5 by the hexagonal orifices 20 inextrusion plate 7 2l. The igniter wafer 22 of solid propellant isprovided with mating orifices 23 and inhibited surfaces 24. FIG- URE 6illustrates protrusion of columns of plastic propellant prior toignition so that the leading plane surface extends beyond the downstreamface of wafer 22, thereby exposing a portion of the upstream lateralsides 26.

FIGURE 7 shows single-oriliced solid propellant annular wafers 40 and 41circumscribing selected individual extrusion orifices 42 and 43 inextrusion plate 44. This configuration has the advantage of reducing theamount of solid propellant burning surface area where such is desirable.The individual annular wafers are each inhibited on all sides except forthe downstream face.

FIGURES 8 and 9 illustrate protective closure of the downstream ends ofWafer orifices :and 31 in solid propellant wafer 32 having inhibitedsurfaces 33, the wafer being bonded to extrusion plate 34 with itsorifices in registry with lextrusion plate yorifices 35 and 36. Thewafer is made of suicient thickness to provide a thin layer 37 of thesolid propellant as a sealing closure across the ends of the waferorifices.

The solid propellant compositions employed in making the igniter waferscan be `any suitable one known in the art which is readily ignited. Itcan, for example, be one of the conventional double-base propellants,eg. nitrocellulose gelatinized with nitroglycerine, or ya composite typepropellant comprising a solid inert fuel, e.g., an inert solid polymer,such as polyvinyl chloride or cellulose acetate, preferably plasticizedwith a non-volatile plasticizer to reduce brittleness, containingdispersed therein a solid oxidizer, such as ammonium perchlorate ornitrate. Many such solid propellants having the different burningproperties required for different applications are available forselection by those skilled in the art.

The monopropellant employed in the devices of this invention ispreferably a plastic mass which is sufficiently cohesive to ret-ain ashaped form and which is extrudable under pressure at ambienttemperatures. Many different plastic monopropellant compositionstailored to different performance requirements can be made having thesedesired physical characteristics. The monopropellant compositionsgenerally preferably comprise a stab-le dispersion of `a finely-divided,insoluble solid oxidizer in a continuous matrix of an oxidizable liquidfuel.

The liquid fuel can be any oxidizable liquid, preferably an organicliquid containing carbon `and hydrogen. Suitable liquid fuels includehydrocarbons, such as triethyl benzene, dodecane, liquidpolyisobutylene, yand the like; compounds containing oxygen linked toacarbon atom, as, for example, esters, like dimethyl maleate, diethylphthalate, dibutyl oxalate, `and the like; alcohols, such as benzylalcohol, triethylene glycol and the like; ethers such as methyla-naphthyl ether `and the like; and many others.

The solid oxidizer can be any suitable, active oxidizing agent whichyields :an oxidizing element such as oxygen, chlorine or fluorinereadily for combustion of the fuel and which is insoluble in the liquidfuel vehicle. Such oxidizers include inorganic oxidizing salts such Iasammonium, sodium and potassium perchlorate or nitrate and metalperoxides such as barium peroxide.

The `amount of solid oxidizer incorporated varies, of course, with theparticular kind and concentration of fuel components in the formulation,the particular oxidizer, and the specific requirements for la given use,in terms, for example, of required heat release and rate of gasgeneration, and can readily be computed by those skilled in the art.Since the liquid vehicle can, in many instances, be loaded with as highas 80 to 90% of finely-divided solids, stoichiometric oxidizer levelswith respect to the fuel components can generally be achieved whendesired, as for example, in rocket applications Where maximum heatrelease and specific impulse are of prime importance. In someapplications, stoichiometric oxidation levels may not be necessary oreven desirable, as, for example, in gas turbines where relatively lowcombustion chamber temperatures are preferred, and the amount ofoxidizer can be correspondingly reduced. Sufficient oxidizer must, ofcourse, be incorporated to maintain active, gas-generating combustion.

Finely-divided solid metal powders such as aluminum or magnesium, may beincorporated in the monopropellant composition :as an additional fuelcomponent along with the liquid fuel. Such metal powders possess theadvantages both of increasing the fuel density and improving thespecific impulse of the monopropellant because of their high heats ofcombustion.

The physical properties of the plastic monopropellant in terms ofshape-retentive cohesiveness, tensile strength and thixotropy, can beimproved by addition of a gelling agent, such as a polymer, e.g.polyvinyl chloride, polyvinyl acetate, cellulose acetate, ethylcellulose, or metal salts of higher fatty acids, such as the sodium ormagnesium stearates or palmitates. Ihe desired physical properties canalso be obtained Without a gelling yagent by using a liquid vehicle ofsubstantial intrinsic viscosity, such as liquid organic polymers, e.g.liquid polyisobutylene, liquid siloxanes, liquid polyesters, and `thelike.

Many different plastic monopropellant compositions may also be used. Itis, therefore, to be understood that this invention is not limited touse with any particular plastic monopropellant composition, but isdirected fto the shaping and ignition of any extruded plasticmonopropellant.

Although this invention has been described with reference toillustra-tive embodiments thereof, it will be apparent to those skilledin `the art that the principles of this invention can be embodied inother forms but Within the scope of the claims.

We claim:

1. In a gas ygenerating apparatus wherein `a plastic monopropellant isextruded from a fuel chamber through an orifice in an apertured memberinto a combustion chamber in the form of a shape-retentive, continuouslyextruding column, the leading face of which is burned in said combustionchamber to generate gases, lthe improvement comprising an igniter waferof `solid propellant mounted on the downstream surface of the aperturedmember and provided with an orifice positioned in registry with saidorifice in said apertured member.

2. In a gas generating apparatus wherein a plastic monopropellant isextruded from a fuel chamber through an orifice in an yapertured memberinto a combustion chamber in the form of a shape-retentive, continuouslyextruding column, the leading face of which is burned in said combustionchamber `to generate gases, the irnprovement comprising an igniter waferof solid propellant mounted on the downstream surface of ythe aperturedmember `and provided with an orifice positioned in registry With saidorifice in said apertured member, the wafer orifice having Wallsparallel to the direction of ow of the palstic monopropellant, saidwafer being inhibited against burning on all surfaces except itsdownstream surface.

3. In a gas generating apparatus wherein a plastic monopropellant isextruded lfrom a fuel chamber through a plurality of orifices in anapertured member into a combustion chamber in the form ofshape-retentive, continuously extruding columns, the leading faces ofwhich are burned in said combustion chamber to generate gases, theimprovement comprising, an igniter wafer of solid propellant mounted tooverlie at least a portion of the downstream surface of the aperturedmember and provided with orifices positioned in registry with all of theorifices in said portion of the apertured member.

4. In a gas generating apparatus wherein a plastic monopropellant isextruded from a fuel chamber through a plurality of orifices in anapertured member into a combustion chamber in the form ofshape-retentive, continuously extruding columns, the leading faces ofwhich are burned in said combustion chamber to generate gases, theimprovement comprising, an igniter wafer of solid propellant mounted tooveriie at least a portion of the downstream surface of the aperturedmember and provided with orifices positioned in registry with all of theextrusion member orifices in said portion of the apertured member, thewafer orifices having walls parallel to the direction of flow of theplastic monopropellant, said Wafer being inhibited against burning onall surfaces eX- cept its downstream surface.

5. ln a gas generating apparatus wherein a plastic monopropellant isextruded from a fuel chamber through an orifice in an apertured memberinto a combustion chamber in the form of a shape-retentive, continuouslyextruding column, the leading face of which is burned in said combustionchamber to generate gases, the in provement comprising an igniter waferof solid propellant mounted on the downstream surface of the aperturedmember and provided with an orifice positioned in registry with saidorifice in said apertured member, the wafer orifice having wallsparallel to the direction of flow of the plastic monopropellant, and atransverse closure overlying its downstream end, said wafer beinginhibited against burning on all surfaces except its downstream surface.

6. In a gas generating apparatus wherein a plastic monopropellant isextruded from a fuel chamber through a plurality of orifices in anapertured member into a combustion chamber in the form ofshape-retentive, continuously extruding columns, the leading faces ofwhich are burned in said combustion chamber to generate gases, theimprovement comprising, an igniter wafer of solid propellant mounted tooverlie at least a portion of the downstream surface of the aperturedmember and provided with orifices positioned in registry with all of theextrusion member orifices in said portion of the apertured member, thewafer orifices having walls parallel to the direction of flow of theplastic monopropellant, and transverse closures overlying theirdownstream ends, said wafer being inhibited against burning on allsurfaces eX- cept its downstream surface.

7. An igniter wafer made of solid propellant for use in a gas generatingapparatus wherein a plastic monopropellant is extruded through anorifice in an apertured member into a combustion chamber in the form ofa shape-retentive, extruding column, the leading face of which is burnedin said combustion chamber to generate gases, said igniter wafer beingadapted for mounting on the downstream surface of the apertured memberand having an orifice designed tobe positioned in registry with saidorifice in said apertured member.

8. An igniter wafer made of solid propellant for use in a gas generatingapparatus wherein a plastic monopropellant is extruded through anorifice in an apertured member into a combustion chamber in the form ofa shape-retentive, extruding column, the leading face of which is burnedin said combustion chamber to generate gases, said igniter wafer beingadapted for mounting on the downstream surface of the apertured memberand having an orifice designed to be positioned in registry with saidorifice in said apertured member, said wafer orifice having wallsparallel to the direction of flow of the plastic monopropellant andsurface-inhibited against burning.

9. An igniter wafer made of solid propellant for use in a gas generatingapparatus wherein a plastic monopropellant is extruded through anorifice in an apertured member into a combustion chamber in the form ofa shape-retentive, extruding column, the leading face of which is burnedin said combustion chamber to generate gases, said igniter wafer beingadapted for mounting on the downstream surface of the apertured memberand having an orifice designed to be positioned in registry with saidorifice in said apertured member, said wafer orifice having wallsparallel to the direction of flow of the plastic monopropellant andsurface-inhibited against burning, and a transverse closure overlyingits downstream end.

l0. An igniter wafer made of solid propellant for use in a gasgenerating apparatus wherein a plastic monopropellant is extrudedthrough -a plurality of orices in an apertured member into a combustionchamber in the form of shape-retentive, extruding columns, the leadingfaces of which are burned in said combustion chamber to generate gases,said igniter wafer being adapted for mounting on the downstream surfaceof the apertured member and having orifices designed to be positioned inregistry with the extrusion orifices in that portion of the aperturedmember over which said Wafer is mounted.

11. An igniter wafer made of solid propellant for use in a gasgenerating apparatus wherein a plastic monopropellant is extrudedthrough a plurality of orifices in an aperttued member into a combustionchamber in the form of shape-retentive, eXtruding columns, the leadingfaces of which are burned in said combustion chamber to generate gases,said igniter wafer being adapted for mounting on the downstream surfaceof the apertured member and having orifices designed to be positioned inregistry with the extrusion orifices in that portion of the aperturedmember over which said wafer is` mounted, Said wafer orifices havingwalls parallel to the direction of flow of the plastic monopropellantand surface-inhibited against burning.

12. An igniter wafer made of solid propellant for use in a gasgenerating apparatus wherein a plastic monopropellant is extrudedthrough a plurality of orifices in an apertured member into a combustionchamber in the form of shape-retentive, extruding columns, the leadingfaces of which are burned in said combustion chamber to generate gases,said igniter wafer being adapted for mounting on the downstream surfaceof the apertured member and having orifices designed to be positioned inregistry with the extrusion orifices in that portion of the aperturedmember over which said wafer is mounted, said wafer orifices havingwalls parallel to the direction of flow of the plastic monopropellantand surfaceinhibited against burning, and transverse closures overlyingtheir downstream ends.

References Cited in the le of this patent UNITED STATES PATENTS 515,500Nobel Feb. 27, 1894 1,506,323 ONeill Aug. 26, 1924 FOREIGN PATENTS582,621 Great Britain Nov. 22, 1946

